Catalyst for methacrylic acid and production and process for producing the same

ABSTRACT

The object of the present invention is to provide a catalyst for producing methacrylic acid in high yield and highly selectively by subjecting methacrolein, isobutylaldehyde or isobutyric acid to gas phase catalytic oxidation, and the preparation method thereof. The catalyst contains Mo, V, P, Cu, Cs and NH 4  as the essential, active components, and the feature is to use for preparing the catalyst a cesium weak acid salt or cesium hydroxide as the Cs raw material and ammonium acetate as the NH 4  raw material. A coated catalyst of the present invention is obtainable by supporting the active component on an inert carrier of alumina or the like.

TECHNICAL FIELD

The present invention relates to a catalyst for producing methacrylicacid by subjecting methacrolein, isobutylaldehyde or isobutyric acid togas phase catalytic oxidation, having a long life, a high activity aswell as high selectivity, and the preparation method thereof.

BACKGROUND ART

A large number of catalysts for producing methacrylic acid by subjectingmethacrolein, isobutylaldehyde or isobutyric acid to gas phase catalyticoxidation, have been proposed. Most of the catalysts thereof are mainlycomposed of molybdenum and phosphorus, and have structures ofheteropolyacids and/or salts thereof. The catalysts used in thereaction, however, have low reaction activities, low selectivity for thedesired substance, and short lives, as compared to molybdenum-vanadiumbased catalysts used in reactions for producing acrylic acid bysubjecting acrolein to gas phase catalytic oxidation, which are known asreactions similar to the reaction for producing methacrylic acid.Accordingly, the improvement of catalytic performance of the catalystsis required although some of the catalysts are industrially utilized.

The present inventors first tried the improvement of low activities, lowselectivity and short lives of conventional gas phase catalyticoxidation catalysts for methacrolein, and found out that gas phasecatalytic oxidation catalysts for methacrolein prepared by the additionof a variety of elements to Mo, V and P, have heteropolyacid (salt)structures and have high activities, high selectivity and areparticularly stable for the time lapse. The inventors propose thecatalysts described in Japanese Patent Publication No. 58-11416,Japanese Patent Publication No. 59-24140, Japanese Patent PublicationNo. 62-14535 and Japanese Patent Publication No. 62-30177.

Recently, because of high concentrations of raw material gases and ofenvironments under which oxidation reactions are conducted at elevatedtemperature, catalysts that exhibit further high activities, highselectivity and long lives, are needed. Various preparation methods areproposed to provide catalysts that satisfy these demands. For example,Japanese Patent Laid-Open No. 5-31368 and Japanese Patent Laid-Open No.8-196908 propose methods for preparing molding catalysts that involveusing NH₄ in addition to the components of Mo, V and P, and utilizingaqueous ammonia as the ammonium source. In addition, Japanese PatentLaid-Open No. 11-226411 describes a method for preparing a moldingcatalyst that comprises using refined starch when an active component ofthe catalyst is granulated, and improving the pore volume of thecatalyst by burning the starch in the calcining step.

Furthermore, when a catalyst is loaded in a fixed-bed reactor as anindustrial catalyst, the catalyst is required to be molded to a constantsize in order to reduce the pressure drop of the reaction gas prior toand subsequent to the catalyst layer. For this purpose, known methodsinvolve normally molding a catalyst powder to a cylindrical material, apellet, a ring-shaped material, a sphere-shaped material, or the like,and impregnating or coating an inert carrier with an active catalystmaterial also.

Advantages of a coated catalyst having the inert carrier as the coreinclude [1] being capable of improving the effective utilization factorof active components of the catalyst, [2] being expected to improve theselectivity due to the homogeneous distribution of the residence time ofreaction materials within the catalyst, and [3] facilitating the removalof the reaction heat on account of the improvement of the catalystthermal conductivity or the dilution effect of the inert carrier. As aresult, there are many examples applied to selective oxidation of alarge heat release.

On the other hand, technical disadvantages in preparing a coatedcatalyst include [1] the peeling of the coating layer and the difficultyof obtaining a mechanically strong catalyst because the catalyst issubject to cracking, [2] the difficulty of coating a carrier with alarge amount of active catalytic material, and [3] the difficulty ofobtaining a highly active catalyst due to inclusion of inert materials.

Methods for overcoming the disadvantages are related to the propertiesof active catalyst substances and the present situation is to studycatalysts individually because of no general techniques.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide a catalyst or a coatedcatalyst for producing methacrylic acid in high yield and highlyselectively by subjecting methacrolein, isobutylaldehyde or isobutyricacid to gas phase catalytic oxidation, and the preparation methodsthereof.

The present inventors have tried to improve the low activities, lowselectivity and short lives of conventional gas phase catalyticoxidation catalysts for methacrolein as a method for solving theabove-mentioned problems, and found out that when preparing a catalystcontaining the essential components of Mo, V, P, Cu, Cs and NH₄, i.e.when preparing a heteropoly acid (salt) containing the essentialcomponents, an industrial catalyst offering a high activity, highselectivity and being particularly stable for the time lapse can beobtained when a cesium weak acid salt or cesium hydroxide is added asthe Cs raw material and ammonium acetate or ammonium hydroxide is addedas the NH₄ raw material, with the completion of the present invention.

That is to say, the present invention relates to:

(1) A catalyst for producing methacrylic acid by subjectingmethacrolein, isobutylaldehyde or isobutyric acid to gas phase catalyticoxidation, having as an active component of the catalyst a heteropolyacid salt comprising a heteropoly acid in which Mo, V, P, Cu, Cs and NH₄are contained as the essential, active components, characterized in thatthe catalyst is obtainable by using a cesium weak acid salt or cesiumhydroxide as the Cs raw material and ammonium acetate as the NH₄ rawmaterial, of the active component of the catalyst.

(2) The catalyst described in (1) above, wherein the Cs raw material iscesium acetate or cesium hydroxide.

(3) The catalyst described in (1) or (2) above, wherein the catalystdoes not contain arsenic as an active component.

(4) The catalyst described in any one of (1) to (3) above, whereincopper acetate or cupric oxide is used as the copper raw material of thecatalyst.

(5) The catalyst described in any one of (1) to (4), wherein thecomposition of the active component of the catalyst is represented bythe formula (1):MO₁₀V_(a)P_(b)Cu_(c)Cs_(d)(NH₄)_(e)X_(f)O_(g)  (1)wherein Mo is molybdenum, V is vanadium, P is phosphorus, Cu is copper,Cs is cesium, (NH₄) is ammonium group, X is one or more elementsselected from the group consisting of Sb, As, Ag, Mg, Zn, Al, B, Ge, Sn,Pb, Ti, Zr, Cr, Re, Bi, W, Fe, Co, Ni, Ce, Th, K and Rb, a to grepresent the atomic ratio of each element, a is a positive number of0.1≦a≦6.0, b is a positive number of 0.5≦b≦6.0, c is a positive numberof 0<c≦3.0, d is a positive number of 0.01≦d≦3.0, e is a positive numberof 0.1≦e≦3.0, f is a positive number of 0≦f≦3.0, and g is a valuedetermined by the oxidation number of an acid of each element.

(6) The catalyst described in (5) above, wherein a is a positive numberof 0.5≦a≦1.2, b is a positive number of 0.9≦b≦1.5, c is a positivenumber of 0.2≦c≦0.8, d is a positive number of 0.2≦d≦0.8, e is apositive number of 1.0≦e≦2.2, and f is a positive number of 0≦f≦0.8.

(7) The catalyst described in (5) or (6) above, wherein the catalystcontains Sb as an essential element.

(8) A method for preparing a catalyst for producing methacrylic acid bysubjecting methacrolein, isobutylaldehyde or isobutyric acid to gasphase catalytic oxidation, the method comprising:

step (A) of blending compounds A-1 to A-3 and, as needed, compound A-4with water to prepare an aqueous solution or dispersion of the compounds(hereinafter, called a slurry, including both),

wherein the compound A-1 is a compound containing Mo, a compoundcontaining V, a compound containing P, and a compound containing Cu, thecompound A-2 is a cesium weak acid salt or cesium hydroxide, thecompound A-3 is ammonium acetate, and the compound A-4 is one or morecompounds selected from the group consisting of compounds containing oneof Sb, As, Ag, Mg, Zn, Al, B, Ge, Sn, Pb, Ti, Zr, Cr, Re, Bi, W, Fe, Co,Ni, Ce, Th, K and Rb; and

step (B) of drying the slurry yielded in step (A) to obtain a driedslurry.

(9) The method for preparing the catalyst described in (8) above,wherein the compound A-4 is used as an essential component.

(10) A method for preparing a coated catalyst for producing methacrylicacid by subjecting methacrolein, isobutylaldehyde or isobutyric acid togas phase catalytic oxidation, the method comprising:

step (a) of blending compounds a-1 to a-3 and, as needed, compound a-4with water to prepare an aqueous solution or dispersion of the compounds(hereinafter, called a slurry, including both),

wherein the compound a-1 is a compound containing Mo, a compoundcontaining V, a compound containing P, and a compound containing Cu, thecompound a-2 is a cesium weak acid salt or cesium hydroxide, thecompound a-3 is ammonium acetate or ammonium hydroxide, and the compounda-4 is one or more compounds selected from the group consisting ofcompounds containing one of Sb, As, Ag, Mg, Zn, Al, B, Ge, Sn, Pb, Ti,Zr, Cr, Re, Bi, W, Fe, Co, Ni, Ce, Th, K and Rb;

step (b) of drying the slurry yielded in step (a) to obtain a driedslurry;

step (c) of coating a carrier with the dried slurry obtained in step (b)using a binder to obtain a coated molded product; and

step (d) of calcining the coated molded product obtained in step (c).

(11) A method for preparing a coated catalyst for producing methacrylicacid by subjecting methacrolein, isobutylaldehyde or isobutyric acid togas phase catalytic oxidation, the method comprising:

step (a) of blending compounds a-1 to a-3 and, as needed, compound a-4with water to prepare a slurry of the compounds, wherein the compounda-1 is a compound containing Mo, a compound containing V, a compoundcontaining P, and a compound containing Cu, the compound a-2 is a cesiumweak acid salt or cesium hydroxide, the compound a-3 is ammonium acetateor ammonium hydroxide, and the compound a-4 is one or more compoundsselected from the group consisting of compounds containing one of Sb,As, Ag, Mg, Zn, Al, B, Ge, Sn, Pb, Ti, Zr, Cr, Re, Bi, W, Fe, Co, Ni,Ce, Th, K and Rb;

step (b) of drying the slurry yielded in step (a) to obtain a driedslurry;

step (b′) of blending the dried slurry obtained in step (b) with a solidcompound containing copper to obtain powders;

step (c) of coating a carrier with the powders obtained in step (b′)using a binder to obtain a coated molded product; and

step (d) of calcining the coated molded product obtained in step (c).

(12) The method for preparing the coated catalyst described in (10) or(11) above, wherein the compound a-4 is used as an essential component.

(13) The method for preparing the coated catalyst described in any oneof (10) to (12) above, wherein at least one species selected from thegroup consisting of water and organic compounds having a boiling pointof 150° C. or lower at one atmospheric pressure is used as a binder.

(14) The method for preparing the coated catalyst described in (13)above, wherein the binder is ethanol.

(15) The method for preparing the coated catalyst described in (13)above, wherein the binder has a weight ratio of ethanol to water beingfrom 10:0 to 5:5.

(16) The method for preparing the coated catalyst described in any oneof (10) to (15) above, wherein the coated molded product is calcined inthe presence of a reducing agent in step (d).

(17) The method for preparing the coated catalyst described in (16)above, wherein the reducing agent is ethanol.

(18) A coated catalyst for producing methacrylic acid by subjectingmethacrolein, isobutylaldehyde or isobutyric acid to gas phase catalyticoxidation, obtainable from the method described in any one of (10) to(17) above.

ADVANTAGES OF THE INVENTION

The catalysts of the present invention are capable of producingmethacrylic acid from methacrolein, isobutylaldehyde or isobutyric acidin high yield and highly selectivity, and further of being used forreactions under high loaded conditions, and thus have extremely largeindustrial values.

BEST MODE FOR CARRYING OUT THE INVENTION

First, a catalyst prepared by using a cerium weak acid salt or ceriumhydroxide and ammonium acetate, a first embodiment of the presentinvention, will be described.

A preferable method for obtaining a catalyst of the present inventioninvolves dissolving and/or dispersing in water a plurality of compoundscontaining each of or a plurality of Mo, V, P, Cu, Cs and NH₄ and, asneeded, other elements (hereinafter, in some cases, the compoundsincluding the active components being also called “activecomponents-containing compound”), using a cesium weak acid salt orcesium hydroxide as a cesium compound and ammonium acetate as anammonium compound when preparing a slurry (step A), and drying theresultant slurry (step B).

In the present invention, an active components-containing compound usedfor preparing a slurry other than that of a cesium weak acid salt,cerium hydroxide and ammonium acetate is preferably a compound thatforms a heteropoly acid or a salt thereof by drying (step B) orcalcining. The compound includes chlorides, sulfates, nitrates, oxidesand acetates, of the active component elements. Preferable examples ofthe compound include nitrates such as potassium nitrate and cobaltnitrate, oxides such as molybdenum oxide, vanadium pentaoxide, antimonytrioxide, cerium oxide, zinc oxide and germanium oxide, and acids (andthe salts thereof) such as orthophosphoric acid, phosphoric acid,arsenic acid, ammonium phosphate and 12-tungstophosphoric acid. Inaddition, use of copper acetates (copper(I) acetate, copper(II) acetate,basic copper acetates, cupric oxide and so forth, preferably copper(II)acetate) sometimes leads to a preferable effect. These may be usedsolely or in a mixture of two or more species.

Cesium weak acid salts are not particularly limited if the salts aresalts between cesium and generally known weak acids. The salts include,for example, cesium hydrogencarbonate, cesium carbonate and cesiumacetate, and cesium acetate is preferable. Additionally, of these,although commercially available cesium acetate can be used directly, forexample, an aqueous cesium acetate solution obtained by adding to anaqueous solution of a water-soluble salt of cesium such as cesiumhydroxide or cesium carbonate one or more equivalents of acetic acid,may also be used.

In the present invention, an active component other than Mo, V, P, Cu,Cs and NH₄ are not particularly limited if the component is a compoundfrom the elements known as the component elements of the catalyst forproducing methacrylic acid. The elements contained in the compoundinclude one or more species selected from the group consisting of Sb,As, Ag, Mg, Zn, Al, B, Ge, Sn, Pb, Ti, Zr, Cr, Re, Bi, W, Fe, Co, Ni,Ce, Th, K and Rb. Of these, the elements excluding As are preferable.

For the ratio of each active component of a catalyst in the presentinvention, based on a molybdenum's atomic ratio of 10, the ratio ofvanadium is normally from 0.1 to 6.0, both inclusive, preferably from0.3 to 2.0, both inclusive, particularly preferably from 0.5 to 1.2,both inclusive, the ratio of phosphorus is normally from 0.5 to 6.0,both inclusive, preferably from 0.9 to 1.5, both inclusive, the ratio ofcopper is normally from 0 exclusive to 3.0 inclusive, preferably from0.01 to 1.0, both inclusive, particularly preferably 0.2 to 0.8, bothinclusive, the ratio of cesium is normally from 0.01 to 3.0, bothinclusive, preferably from 0.1 to 1.5, both inclusive, particularlypreferably from 0.2 to 1.0, both inclusive, the ratio of ammonium isnormally from 0.1 to 3.0, both inclusive, preferably from 0.5 to 3.0,both inclusive, particularly preferably from 1.0 to 2.2, both inclusive.The kinds and the use ratios of other active components necessary foruse are determined, as appropriate, in such a way that a catalyst havingthe best suitable performance is obtainable, in accordance with the useconditions, etc. of the catalyst. A preferable catalyst used undernormal conditions is one having an active component compositionrepresented by the formula (1):MO₁₀V_(a)P_(b)Cu_(c)Cs_(d)(NH₄)_(e)X_(f)O_(g)  (1)wherein Mo is molybdenum, V is vanadium, P is phosphorus, Cu is copper,Cs is cesium, (NH₄) is ammonium group, X is one or more elementsselected from the group consisting of Sb, As, Ag, Mg, Zn, Al, B, Ge, Sn,Pb, Ti, Zr, Cr, Re, Bi, W, Fe, Co, Ni, Ce, Th, K and Rb, a to grepresent the atomic ratio of each element, a is a positive number of0.1≦a≦6.0, b is a positive number of 0.5≦b≦6.0, c is a positive numberof 0<c≦3.0, d is a positive number of 0.01≦d≦3.0, e is a positive numberof 0.1≦e≦3.0, f is a positive number of 0≦f≦3.0, and g is a valuedetermined by the oxidation number of each element. In addition, theactive component composition thereof means the component in the driedslurry below and does not necessarily reflect the composition of thepowder via step (d). Namely, because of a calcining temperature and acalcining time in the calcining step (step (d)), NH₄ component mayevaporate and be substituted with a hydrogen or metal atom. According tothe findings of the present inventors, NH₄ component in the dried slurrysometimes evaporates by passing through the calcining step. Theevaporation level of NH₄ depends on a calcining temperature, calciningtime and calcining atomosphere, i.e. under the air or nitrogen, andreaches up to about 90 mole %.

In the formula (1) above, element X is preferably Sb. Sb is used, asnecessary, in the range of 0 to 2.2, both inclusive, preferably from0.01 to 0.8, both inclusive, in the formula (1) above.

The catalyst can be obtained in the following procedure.

First, an aqueous solution or dispersion of the activecomponents-containing compound (hereinafter, called a slurry, includingboth) is prepared. The slurry can be obtained by uniformly blending aplurality of compounds containing each active component with a solvent,preferably water. The slurry preferably contains all the compoundscontaining necessary active components in the needed amount of catalyst.The order of addition of compounds containing active components when theslurry is prepared is not specifically limited, but it is preferablethat, first, compounds containing Mo, V and P are made a slurry and thento the slurry are added a compound containing a cesium weak acid salt orcesium hydroxide, ammonium acetate and copper.

The temperature when the slurry is prepared is not particularly limitedunless causing troubles, and the temperature when a cesium weak acidsalt or cesium hydroxide, ammonium acetate and a copper-containingcompound is normally from 0 to 35° C., preferably from 10 to 30° C.,which sometimes results in making the resultant catalyst highly active.The tendency is remarkable when copper acetate is used as acopper-containing compound, and so the adoption of the above-mentioned,preferable method of addition for preparing a slurry is ratherefficient.

In the present invention, a slurry is preferably an aqueous solution.The use ratio of a compound containing each active component in a slurryis not particularly limited if the atomic ratio of each active componentis within the above-described range. The amount of use of water is notparticularly limited if compounds to be used can be dissolved completelyor homogeneously blended, and is determined taking into account thedrying method, drying conditions, etc. described below. That is, theamount of water is about 200 to 2000 parts by weight, based on the totalamount, 100 parts by weight, of compounds for preparing a slurry.Although a large amount of water may be usable, but the amount much morethan the normal amount leads to many demerits, including a high energycost in the drying step as well as sometimes causing incomplete drying,and so the suitable amount is preferable.

Next, the slurry obtained above is dried to be made a dried slurry. Amethod for drying is not particularly limited if the slurry cancompletely be dried, and, methods include, for example, drum drying,freeze drying, spray drying, and evaporation drying. Of these, in thepresent invention, the spray drying, which allows a slurry state to dryto a powder or a granule in a short time, and the evaporation drying,which directly dries the slurry simply and easily, are preferable, andthe evaporation drying is particularly preferable.

The temperature of the spray drying varies depending on theconcentration and the transport rate of a slurry, and the temperature ofthe exit of a drier is generally from 70 to 150° C. In addition, theaverage particle diameter of the resultant dried slurry is preferablydried to be from about 30 to 500 μm. The evaporation drying may becarried out according to the standard method, and in this case a driedslurry is obtained as clusters or as large particles, and thus isground, as appropriate, for use such that the size is preferably 300 μmor less. In the present invention, a dried slurry includes such a groundslurry.

The dried slurry obtained in this way can be utilized for gas phasecatalytic oxidation as a catalyst of the present invention and, asdescribed previously, the slurry is preferably formed into a cylindricalmaterial, a pellet, a ring-shaped material or sphere-shaped material forthe purpose of reducing the pressure loss of reaction gas. For these,due to being expected to improve selectivity and remove reaction heat,it is particularly preferable that an inert carrier is coated with thedried slurry to obtain a coated catalyst. Furthermore, in step (A) aslurry is prepared without using a copper-containing compound, and theslurry is supplied to the drying step, and then the resultant driedmaterial is blended with a powder of the copper-containing compound tobe able to obtain a catalyst of the present invention as well.

In the following, a method for preparing a coated catalyst, a secondembodiment of the present invention, will be set forth.

A coated catalyst of the present invention can be prepared as for thepreparation of the dried slurry described above except that ammoniumhydroxide can further be selected as an ammonium source in step (A). Inother words, raw compounds are dissolved and/or dispersed in water toprepare a slurry (step (a)) and this is dried to obtain a dried slurry(step (b)). In step (a) the order of addition of each raw compound isnot particularly restricted, but as in step (A) it is rather preferablethat compounds containing Mo, V and P are first made a slurry, andsubsequently compounds to be a cesium source, an ammonium source and acopper source are added to the slurry. For step (a) as well, thetemperature when a cesium source, an ammonium source and a copper sourceare added is normally from 0 to 35° C., preferably from 10 to 30° C.

Additionally, in step (a) a slurry is prepared without using acopper-containing compound, and the slurry is supplied to the dryingstep, and then the resultant dried material is blended with a powder ofthe copper-containing compound to obtain a mixture (step (b′)), fromwhich a coated catalyst of the present invention can be obtained aswell.

The resultant dried slurry (or the mixture described above, hereinafter,the dried slurry includes the above-mentioned mixture) is supplied tothe coating step described below (step c)).

For the coating step (step (c)) the rolling granulating processdescribed below is preferable. This process involves vigorouslyagitating, for example, using a device having an even or uneven disc atthe bottom of a fixed vessel, a carrier in the vessel by rotating thedisc at a high speed and thus repeating the rotation and revolution ofthe carrier and adding to this an mixture of a binder and a dried slurryand, as needed, other additives, such as a molding aid and astrength-improving material, to coat the carrier with the mixture.Methods of adding a binder can adopt any method of [1] adding in advancethe above-mentioned mixture to the binder, [2] adding the bindersimultaneously with adding the mixture to the fixed vessel, [3] addingthe binder after adding the mixture to the fixed vessel, [4] adding thebinder prior to adding the mixture to the fixed vessel, [5] separatingthe mixture and the binder and adding the total amount in a combinationof, as appropriate, [2] to [4]. Of these, for [5], for example, thespeed of addition is preferably adjusted with an auto-feeder or the likein such a manner that a specified amount of mixture is supported on thecarrier without adherence of the mixture on the fixed vessel wall andcoagulation of the mixture particles with each other.

A binder is not particularly limited if it is at least one speciesselected from the group consisting of water and organic compounds havinga boiling point of 150° C. or lower at one atmospheric pressure, and abinder having a boiling point of 100° C. or lower is preferableconsidering drying after coating, etc. Examples of binders except waterinclude alcohols such as methanol, ethanol, propanols and butanols,preferably alcohols having a carbon number of 1 to 4, ethers such asethyl ether, butyl ether and dioxane, esters such as ethyl acetate andbutyl acetate, ketones such as acetone and methyl ethyl ketone, andaqueous solutions thereof, and ethanol is particularly preferable. Whenethanol is used as a binder, the ratio by weight of ethanol to water isfrom 10:0 to 5:5, preferably from 10:0 to 7:3, particularly preferablyabout 10 to 30% by weight in ethanol concentration. The amount of use ofa binder is normally from 2 to 60 parts by weight, preferably from 5 to25 parts by weight, based on 100 parts by weight of a dried slurry.

Examples of carriers capable of being used in the present inventioninclude silicon carbide, alumina, silica alumina, mullite, and alundum,which are sphere carriers and have a diameter of from 1 to 15 mm,preferably from 2.5 to 10 mm, and particularly preferably from 2.5 to4.5 mm. The pore ratio of carrier for use is normally from 10 to 70%.The pore ratio of carrier is defined as (W₃−W₁)/(W₃−W₂)*100, wherein W₁is a dry carrier weight, W₂ is a carrier weight in water, and W₃ is acarrier weight at saturation with water absorbed. The ratio of a coatingdried slurry to (the dried slurry+a carrier) is normally from 10 to 75%by weight, preferably from 15 to 60% by weight.

When the ratio of a coating dried slurry is large, the reaction activityof the coated catalyst tends to become large, but the mechanicalstrength tends to be small (the degree of friction being large).Inversely, when the ratio of a coating dried slurry is small, themechanical strength is prone to be large (the degree of friction beingsmall), but the reaction activity is prone to be small.

In the present invention, when a carrier is coated with a dried slurry,a molding aid such as silica gel, diatomite or an alumina powder mayfurther be used, as needed. The amount of molding aid for use isnormally from 5 to 60 parts by weight based on 100 parts by weight ofthe dried slurry.

In addition, use of additional, as needed, inorganic fibers such asceramic fibers and whisker as a strength-improving material is useful toimprove the mechanical strength of the catalyst. However, fibers, whichreact with catalyst components, such as potassium titanate whisker andbasic magnesium carbonate whisker are unsuitable. The amount of use ofthe fibers is normally from 1 to 30 parts by weight based on 100 partsby weight of the dried slurry.

Additives such as the molding aid and the strength-improving materialabove are introduced into a granulating machine normally in the coatingstep along with a carrier, a dried slurry, a binder, etc. to be used tocoat the carrier.

In this way, a carrier is coated with a dried slurry, and the coatedproduct obtained normally has a diameter of about 3 to 15 mm, preferablyabout 3.2 to 5 mm.

A coated catalyst obtained in this way can directly be supplied to gasphase catalytic oxidation as a catalyst. It is preferable that thecatalyst is calcined (step (d)), sometimes causing the improvement ofthe catalyst activity. In this case, the calcining temperature isnormally from 100 to 420° C., preferably from 250 to 400° C. and thecalcining time is from 1 to 20 hours.

In addition, calcining is normally carried out under an aerialatmosphere, may be conducted under an inert gas atmosphere, or aftercalcining under an inert gas atmosphere, additional calcining, asrequired, may be performed under an aerial atmosphere. Furthermore, itis preferable that calcining is carried out under an inert gasatmosphere, preferably in the presence of a reducing agent, whichsometimes leads to obtaining a catalyst with a higher activity. Areducing agent is not particularly limited if the agent preferablybecomes gaseous at the calcining temperature. Examples of reducingagents include CO, alcohols having a carbon number of 2 to 5, aldehydes,ketones and organic acids, and ethanol is particularly preferable.

A catalyst of the present invention obtained as described above is usedwhen methacrylic acid is produced by subjecting methacrolein,isobutylaldehyde or isobutyric acid to gas phase catalytic oxidation.Additionally, catalysts of the present invention include, unlessotherwise stated, both a dried slurry obtained via steps (A) and (B) anda coated catalyst obtained via steps (a) to (c) (and preferably furthervia step (d)).

Hereinafter, a gas phase catalytic reaction of methacrolein, which isthe most preferable raw material in the case of using a catalyst of thepresent invention, will be set forth.

Molecular oxygen or a gas containing molecular oxygen is used for gasphase catalytic oxidation. The molar ratio, for use, of molecular oxygento methacrolein is preferably from 0.5 to 20, particularly preferablyfrom 1 to 10. Water is preferably introduced into raw material gases ina molar ratio of water to methacrolein being from 1 to 20 in order toallow the reaction to smoothly proceed.

The raw material gases may contain oxygen and, as needed, inert gases,such as nitrogen, carbon dioxide gas and saturated hydrocarbon, inaddition to water (normally contained as water vapor).

Further, for methacrolein, gas obtained by oxidizing isobutylene,tertiary butanol and methyl tertiary butylether may directly besupplied.

The reaction temperature of the gas phase catalytic oxidation isnormally from 200 to 400° C., preferably from 260 to 360° C. With theamount of supply of raw material gases, the space velocity (SV) isnormally from 100 to 6000 hr⁻¹, preferably from 400 to 3000 hr⁻¹.

Use of a catalyst of the present invention does not change the reactionmerit even though the SV is increased, and allows the reaction toproceed at a high space velocity.

In addition, the catalytic oxidation is possible at an increasedpressure or at a reduced pressure as well, and a pressure near anatmospheric pressure is normally suitable.

EXAMPLES

Hereinafter, the present invention will be described furtherspecifically using Examples and Comparative Examples.

Additionally, in Examples and Comparative Examples below, the degree ofconversion, selectivity and yield are defined as follows:Conversion degree=(molar number of reacted methacrolein/molar number ofsupplied methacrolein)×100Selectivity=(molar number of produced methacrolein/molar number ofreacted methacrolein)×100Yield=(molar number of produced methacrolein/molar number of suppliedmethacrolein)×100

Furthermore, the catalytic, active components composition in theExamples all are ratios calculated from loaded raw materials. Inaddition, Formulae are indicated without oxygen.

Example 1

1) Preparation of Catalyst

To 1200 mL of purified water were added 200 g of molybdenum trioxide,8.84 g of vanadium pentaoxide and 17.61 g of 85 wt % orthophosphoricacid, and the solution was heated at reflux at 90 to 100° C. for fivehours to yield a reddish-brown, transparent solution.

Subsequently, to the solution was added 6.07 g of antimony trioxide andthe resultant solution was further heated at reflux at 90 to 100° C. fortwo hours to obtain an antimony trioxide-dissolved, highly dark bluesolution.

Then, the resulting solution was cooled to from 15 to 20° C. To thesolution were gradually added a solution of 13.33 g of cesium acetatedissolved in 150 mL of purified water and a solution of 16.06 g ofammonium acetate dissolved in 150 mL of purified water at the same timewith agitation. Then, to the slurry was further added a solutionprepared by dissolving 11.09 g of cupric acetate monohydrate in 170 mLof purified water and the resultant solution was aged at 15 to 20° C.for one hour to yield a green blue slurry.

Then, the resultant slurry was heated in a water bath to be evaporatedand dried. The residue was ground with a mortar to cause the size to be300 μm or less, thereby yielding a dried slurry. The composition of theresultant dried slurry is:Mo₁₀V_(0.7)P_(1.1)Cu_(0.4)Sb_(0.3)Cs_(0.5)(NH₄)_(1.5)

Then, 215.9 g of the resultant dried slurry was uniformly blended with29.8 g of a strength-improving material (ceramic fiber), and 200 g of aspherical, porous alumina carrier (particle diameter of 3.5 mm, poreratio of 25.5%) was coated with the resulting mixture leading to acoated molded product using an aqueous 90 wt % ethanol solution as abinder by coating-mold by means of the rolling granulating process.During this process, the loss of powder was rarely observed.

Subsequently, the resultant coated molded product was calcined under aflow of air at 310° C. for five hours, thereby yielding a coatedcatalyst of the present invention. The particle diameter of the coatedcatalyst obtained was 4.3 mm (average value).

2) Catalytic Oxidation of Methacrolein

Into a stainless steel reaction tube with an inside diameter of 18.4 mmwas introduced 10.3 mL of the resultant coated catalyst, and theoxidation of methacrolein was carried out at a space velocity (SV) of1200 hr⁻¹ and at a reaction bath temperature of 310° C., with a rawmaterial composition in terms of the molar ratio of methacrolein tooxygen to water vapor to nitrogen being 1:2.0:4.0:18.6. First, thereaction results were determined at a reaction bath temperature of 310°C., and then the reaction bath temperature was risen to 350° C. and areaction was allowed to continue for another 15 hours. Then, thereaction bath temperature was decreased to 310° C. and the reactionresults were determined. Table 1 shows the reaction results. TABLE 1Conversion Selectivity Yield PT(° C.) degree (%) (%) (%) Initial stageof reaction 330 70.0 83.8 58.7 After 15 hr at 350°C. 327 83.4 83.1 69.3* Pt: Peak or Highest Temperature (the same in Tables below)* Conversion degree: conversion degree of methacrolein (the same inTables below)* Selectivity: selectivity of methacrolein (the same in Tables below)* Yield: yield of methacrolein (the same in Tables below)

Example 2

1) Preparation of Catalyst

To 2500 mL of purified water were added 350 g of molybdenum trioxide,17.69 g of vanadium pentaoxide and 32.27 g of 85 wt % orthophosphoricacid, and the solution was heated at reflux at 90 to 100° C. for fivehours to yield a reddish-brown, transparent solution.

Subsequently, to the solution was added 17.71 g of antimony trioxide andthe resultant solution was further heated at reflux at 90 to 100° C. fortwo hours to obtain an antimony trioxide-dissolved, highly dark bluesolution.

Then, the resulting solution was cooled to from 15 to 20° C. To thesolution were gradually added a solution of 23.33 g of cesium acetatedissolved in 170 mL of purified water and a solution of 33.73 g ofammonium acetate dissolved in 170 mL of purified water at the same timewith agitation and the resultant solution was aged at 15 to 20° C. forone hour to yield a green blue slurry.

Then, the resultant slurry was heated in a water bath to be evaporatedand dried. The residue was ground with a mortar to cause the size to be300 μm or less, thereby yielding a powder. The composition of theresultant powder is:Mo₁₀V_(0.8)P_(1.15)Sb_(0.4)Cs_(0.5)(NH₄)_(1.8)

Then, to the powder above were added 19.41 g of a powder of cupricacetate monohydrate in which the atomic ratio of the Cu to the Mo is0.4:10 and 66.1 g of a strength-improving material (ceramic fiber), andthe resulting material was mixed uniformly, and then 444.1 g of aspherical, porous alumina carrier (particle diameter of 3.5 mm, poreratio of 25.5%) was coated with the resulting mixture leading to acoated molded product using an aqueous 90 wt % ethanol solution as abinder by coating-mold by means of the rolling granulating process. Theparticle diameter of the coated catalyst obtained was 4.3 mm (averagevalue).

The resultant coated molded product was calcined at 380° C. for 10 hoursusing ethanol (20 g/h) as a reducing agent under a flow of nitrogen (5L/min) with a box-shaped hot-air circulating calcining furnace to yielda coated catalyst of the present invention. The active componentscomposition of the resulting coated catalyst is:Mo₁₀V_(0.8)P_(1.15)Cu_(0.4)Sb_(0.4)Cs_(0.5)(NH₄)_(1.8)

2) Catalytic Oxidation of Methacrolein

As in Example 1 except using the resultant coated catalyst, oxidationwas carried out. The reaction results are indicated in Table 2. TABLE 2Conversion Selectivity Yield PT(° C.) degree (%) (%) (%) Initial stageof reaction 327 86.5 76.8 66.5 After 15 hr at 350° C. 323 85.2 86.4 73.6

Example 3

1) Preparation of Catalyst

To 1400 mL of purified water were added 200 g of molybdenum trioxide,10.11 g of vanadium pentaoxide and 18.42 g of 85 wt % orthophosphoricacid, and the solution was heated at reflux at 90 to 100° C. for fivehours to yield a reddish-brown, transparent solution.

Then, the resulting solution was cooled to from 15 to 20° C. To thesolution were gradually added a solution of 13.33 g of cesium acetatedissolved in 100 mL of purified water and a solution of 19.27 g ofammonium acetate dissolved in 100 mL of purified water at the same timewith agitation and the resultant solution was aged at 15 to 20° C. forone hour to yield a green blue slurry.

Then, the resultant slurry was heated in a water bath to be evaporatedand dried. The residue was ground with a mortar to cause the size to be300 μm or less, thereby yielding a powder. The composition of theresultant powder is:Mo₁₀V_(0.8)P_(1.15)Cs_(0.5)(NH₄)_(1.8)

Then, to the powder above were added 11.09 g of a powder of cupricacetate monohydrate in which the atomic ratio of the Cu to the Mo is0.4:10 and 28.9 g of a strength-improving material (ceramic fiber), andthe resulting material was mixed uniformly, and then 200 g of aspherical, porous alumina carrier (particle diameter of 3.5 mm, poreratio of 25.5%) was coated with the resulting mixture leading to acoated molded product using an aqueous 90 wt % ethanol solution as abinder by coating-mold by means of the rolling granulating process. Theparticle diameter of the coated catalyst obtained was 4.3 mm (averagevalue).

The resultant coated molded product was calcined at 380° C. for 10 hourswith ethanol (20 g/h) as a reducing agent under a flow of nitrogen (5L/min) using a box-shaped hot-air circulating calcining furnace to yielda coated catalyst of the present invention. The active componentscomposition of the resulting coated catalyst is:Mo₁₀V_(0.8)P_(1.15)Cu_(0.4)Cs_(0.5)(NH₄)_(1.8)

2) Catalytic Oxidation of Methacrolein

As in Example 1 except using the resultant coated catalyst, oxidationwas carried out. The reaction results are indicated in Table 3. TABLE 3Conversion Selectivity Yield PT(° C.) degree (%) (%) (%) Initial stageof reaction 325 83.5 80.2 66.9 After 15 hr at 350° C. 323 84.9 83.4 70.3

Comparative Example 1

1) Preparation of Catalyst

To 1500 mL of purified water were added 200 g of molybdenum trioxide,8.84 g of vanadium pentaoxide and 18.42 g of 85 wt % orthophosphoricacid, and the solution was heated at reflux at 90 to 100° C. for fivehours to yield a reddish-brown, transparent solution.

Subsequently, to the solution was added 6.07 g of antimony trioxide andthe resultant solution was further heated at reflux at 90 to 100° C. fortwo hours to obtain an antimony trioxide-dissolved, highly dark bluesolution.

Then, the resulting solution was cooled to from 15 to 20° C. To thesolution were gradually added a solution of 13.54 g of cesium nitratedissolved in 200 mL of purified water and a solution of a 28% aqueousammonia solution (26.08 g) diluted in 150 mL of purified water at thesame time with agitation and the resultant solution was aged at 15 to20° C. for one hour to yield a green blue slurry.

Then, the resultant slurry was heated in a water bath to be evaporatedand dried. The residue was ground with a mortar to cause the size to be300 μm or less, thereby yielding a powder. The composition of theresultant powder is:Mo₁₀V_(0.7)P_(1.15)Sb_(0.3)Cs_(0.5)(NH₄)_(1.5)

Then, to the powder above were added 11.09 g of a powder of cupricacetate monohydrate in which the atomic ratio of the Cu to the Mo is0.4:10 and 34.7 g of a strength-improving material (ceramic fiber), andthe resulting material was mixed uniformly, and then 232.6 g of aspherical, porous alumina carrier (particle diameter of 3.5 mm, poreratio of 25.5%) was coated with the resulting mixture leading to acoated molded product using an aqueous 90 wt % ethanol solution as abinder by coating-mold by means of the rolling granulating process. Theparticle diameter of the coated molded product obtained was 4.3 mm(average value).

The resultant coated molded product was calcined at 310° C. for fivehours under a flow of air to yield a coated catalyst for comparison. Thecomposition of the resulting coated catalyst is:Mo₁₀V_(0.7)P_(1.15)Cu_(0.4)Sb_(0.3)Cs_(0.5)(NH₄)_(1.5)

2) Catalytic Oxidation of Methacrolein

The resultant coated catalyst was subjected to oxidation as in Example 1with the exception that the reaction bath temperature was 310° C. only.The reaction results are shown in Table 4. TABLE 4 PT(° C.) Conversiondegree (%) Selectivity (%) Yield (%) 319 33.0 74.6 24.6

Example 4

A coated catalyst of the present invention was obtained as in the caseof Example 2 with the exception that the amount of antimony trioxide waschanged into 22.14 g, that the amount of ammonium acetate was changedinto 26.23 g, and that calcining step conditions were changed into beingunder a flow of air at 310° C. for five hours. The particle diameter ofthe resultant coated catalyst was 4.3 mm (average value).

Example 5

A coated catalyst of the present invention was obtained as in the caseof Example 2 with the exception that the amount of vanadium pentaoxidewas changed into 15.48 g, that the amount of 85 wt % orthophosphoricacid was changed into 31.71 g, that the amount of ammonium acetate waschanged into 31.86 g, and that calcining step conditions were changedinto being under a flow of air at 310° C. for five hours. The particlediameter of the resultant coated catalyst was 4.3 mm (average value).

Example 6

A coated catalyst of the present invention was obtained as in the caseof Example 2 with the exception that a solution of 23.33 g of cesiumacetate in 170 mL water was changed into a solution of 20.41 g of cesiumhydroxide monohydrate in 175 mL water (the ratio of Cs:Mo being 0.5:10).The particle diameter of the resultant coated catalyst was 4.3 mm(average value).

Example 7

A coated catalyst of the present invention was obtained as in the caseof Example 2 with the exception that a solution of 23.33 g cesiumacetate in 170 mL water was changed into a solution prepared by adding asolution of 7.30 g of acetic acid in 52.5 mL water to a solution of20.41 g of cesium hydroxide monohydrate in 123 mL water. The particlediameter of the resultant coated catalyst was 4.3 mm (average value).

Example 8

A coated catalyst of the present invention was obtained as in the caseof Example 2 with the exception that the amount of antimony trioxide waschanged into 2.21 g. The particle diameter of the resultant coatedcatalyst was 4.3 mm (average value).

Example 9

A coated catalyst of the present invention was obtained as in the caseof Example 3 with the exception that the amount of ammonium acetate waschanged into 21.41 g, and that antimony trioxide was not used. Theparticle diameter of the resultant coated catalyst was 4.3 mm (averagevalue).

Example 10

A coated catalyst of the present invention was obtained as in the caseof Example 2 with the exception that the cooling temperature of theantimony trioxide-dissolved, highly dark blue solution was changed into26 to 30° C. The particle diameter of the resultant coated catalyst was4.3 mm (average value).

Comparative Example 2

A coated catalyst for comparison was obtained as in the case ofComparative Example 1 with the exception that ammonium acetate was notused, and that the amounts of 85 wt % orthophosphoric acid and antimonytrioxide were changed into 20.09 g and 8.09, respectively. The particlediameter of the resultant coated catalyst was 4.3 mm (average value).

Comparative Example 3

A coated catalyst for comparison was obtained as in the case of Example2 with the exception that cesium acetate and ammonium acetate were notused, and that the amount of cupric acetate monohydrate was changed into24.26 g. The particle diameter of the resultant coated catalyst was 4.3mm (average value).

Comparative Example 4

A coated catalyst for comparison was obtained as in the case of Example2 with the exception that cesium acetate was not used. The particlediameter of the resultant coated catalyst was 4.3 mm (average value).

Comparative Example 5

A coated catalyst for comparison was obtained as in the case ofComparative Example 1 with the exception that the amount of 85 wt %orthophosphoric acid was changed into 19.22 g, and that 13.54 g ofcesium nitrate was changed into 7.02 g of potassium acetate. Theparticle diameter of the resultant coated catalyst was 4.3 mm (averagevalue).

Comparative Example 6

A coated catalyst for comparison was obtained as in the case ofComparative Example 1 with the exception that the amount of 85 wt %orthophosphoric acid was changed into 19.22 g, and that 13.54 g ofcesium nitrate was changed into 10.25 g of rubidium acetate. Theparticle diameter of the resultant coated catalyst was 4.3 mm (averagevalue).

Test Example

The coated catalysts obtained from Examples 4 to 10 and ComparativeExamples 2 to 6 were oxidized as in the case of Example 1 at a bathtemperature of 350° C. for 15 hours, and subsequently the bathtemperature was decreased to 310° C. and the reaction attributes weredetermined. The results are shown in Table 5 together with the atomicratio of each catalyst active component of the coated catalysts. TABLE 5Catalyst performance Catalyst active components composition PTConversion Selectivity Yield Mo V P Cu Cs NH₄ Sb (° C.) degree (%) (%)(%) Example 4 10 0.8 1.15 0.4 0.5 1.4 0.5 323 85.0 83.9 71.4 Example 510 0.7 1.13 0.4 0.5 1.7 0.4 317 89.0 79.7 70.9 Example 6 10 0.8 1.15 0.40.5 1.8 0.4 322 81.9 86.4 70.8 Example 7 10 0.8 1.15 0.4 0.5 1.8 0.4 32383.6 85.1 71.1 Example 8 10 0.8 1.15 0.4 0.5 1.8 0.05 321 80.6 85.6 69.0Example 9 10 0.8 1.15 0.4 0.5 2.0 — 322 80.2 86.3 69.2 Example 10 10 0.81.15 0.4 0.5 1.8 0.4 323 83.7 85.0 71.2 Comparative 10 0.7 1.2 0.4 0.5 —0.4 331 88.7 70.8 62.8 Example 2 Comparative 10 0.8 1.15 0.5 — — 0.4 32060.7 79.2 48.1 Example 3 Comparative 10 0.8 1.15 0.4 — 1.8 0.4 311 10.153.0 5.3 Example 4 Comparative 10 0.7 1.2 0.4 0.5 1.5 0.3 312 11.1 65.47.2 Example 5 (K) Comparative 10 0.7 1.2 0.4 0.5 1.5 0.3 314 35.6 85.530.5 Example 6 (Rb)

1. A catalyst for producing methacrylic acid by subjecting methacrolein,isobutylaldehyde or isobutyric acid to gas phase catalytic oxidation,having as an active component of the catalyst a heteropoly acid saltcomprising a heteropoly acid in which Mo, V, P, Cu, Cs and NH₄ arecontained as the essential, active components, characterized in that thecatalyst is obtainable by using a cesium weak acid salt or cesiumhydroxide as the Cs raw material and ammonium acetate as the NH₄ rawmaterial, of the active component of the catalyst.
 2. The catalystaccording to claim 1, wherein the Cs raw material is cesium acetate orcesium hydroxide.
 3. The catalyst according to claim 1 or 2, wherein thecatalyst does not contain arsenic as an active component.
 4. Thecatalyst according to any one of claims 1 to 3, wherein copper acetateor cupric oxide is used as the copper raw material of the catalyst. 5.The catalyst according to any one of claims 1 to 4, wherein thecomposition of the active component of the catalyst is represented bythe formula (1):MO₁₀V_(a)P_(b)Cu_(c)Cs_(d)(NH₄)_(e)X_(f)O_(g)  (1) wherein Mo ismolybdenum, V is vanadium, P is phosphorus, Cu is copper, Cs is cesium,(NH₄) is ammonium group, X is one or more elements selected from thegroup consisting of Sb, As, Ag, Mg, Zn, Al, B, Ge, Sn, Pb, Ti, Zr, Cr,Re, Bi, W, Fe, Co, Ni, Ce, Th, K and Rb, a to g represent the atomicratio of each element, a is a positive number of 0.1≦a≦6.0, b is apositive number of 0.5≦b≦6.0, c is a positive number of 0<c≦3.0, d is apositive number of 0.01≦d≦3.0, e is a positive number of 0.1≦e≦3.0, f isa positive number of 0≦f≦3.0, and g is a value determined by theoxidation number of an acid of each element.
 6. The catalyst accordingto claim 5, wherein a is a positive number of 0.5≦a≦1.2, b is a positivenumber of 0.9≦b≦1.5, c is a positive number of 0.2≦c≦0.8, d is apositive number of 0.2≦d≦0.8, e is a positive number of 1.0≦e≦2.2, and fis a positive number of 0≦f≦0.8.
 7. The catalyst according to claim 5 or6, wherein the catalyst contains Sb as an essential element.
 8. A methodfor preparing a catalyst for producing methacrylic acid by subjectingmethacrolein, isobutylaldehyde or isobutyric acid to gas phase catalyticoxidation, the method comprising: step (A) of blending compounds A-1 toA-3 and, as needed, compound A-4 with water to prepare an aqueoussolution or dispersion of the compounds (hereinafter, called a slurry,including both), wherein the compound A-1 is a compound containing Mo, acompound containing V, a compound containing P, and a compoundcontaining Cu, the compound A-2 is a cesium weak acid salt or cesiumhydroxide, the compound A-3 is ammonium acetate, and the compound A-4 isone or more compounds selected from the group consisting of compoundscontaining one of Sb, As, Ag, Mg, Zn, Al, B, Ge, Sn, Pb, Ti, Zr, Cr, Re,Bi, W, Fe, Co, Ni, Ce, Th, K and Rb; and step (B) of drying the slurryyielded in step (A) to obtain a dried slurry.
 9. The method forpreparing the catalyst according to claim 8, wherein the compound A-4 isused as an essential component.
 10. A method for preparing a coatedcatalyst for producing methacrylic acid by subjecting methacrolein,isobutylaldehyde or isobutyric acid to gas phase catalytic oxidation,the method comprising: step (a) of blending compounds a-1 to a-3 and, asneeded, compound a-4 with water to prepare an aqueous solution ordispersion of the compounds (hereinafter, called a slurry, includingboth), wherein the compound a-1 is a compound containing Mo, a compoundcontaining V, a compound containing P, and a compound containing Cu, thecompound a-2 is a cesium weak acid salt or cesium hydroxide, thecompound a-3 is ammonium acetate or ammonium hydroxide, and the compounda-4 is one or more compounds selected from the group consisting ofcompounds containing one of Sb, As, Ag, Mg, Zn, Al, B, Ge, Sn, Pb, Ti,Zr, Cr, Re, Bi, W, Fe, Co, Ni, Ce, Th, K and Rb; step (b) of drying theslurry yielded in step (a) to obtain a dried slurry; step (c) of coatinga carrier with the dried slurry obtained in step (b) using a binder toobtain a coated molded product; and step (d) of calcining the coatedmolded product obtained in step (c).
 11. A method for preparing a coatedcatalyst for producing methacrylic acid by subjecting methacrolein,isobutylaldehyde or isobutyric acid to gas phase catalytic oxidation,the method comprising: step (a) of blending compounds a-1 to a-3 and, asneeded, compound a-4 with water to prepare a slurry of the compounds,wherein the compound a-1 is a compound containing Mo, a compoundcontaining V, a compound containing P, and a compound containing Cu, thecompound a-2 is a cesium weak acid salt or cesium hydroxide, thecompound a-3 is ammonium acetate or ammonium hydroxide, and the compounda-4 is one or more compounds selected from the group consisting ofcompounds containing one of Sb, As, Ag, Mg, Zn, Al, B, Ge, Sn, Pb, Ti,Zr, Cr, Re, Bi, W, Fe, Co, Ni, Ce, Th, K and Rb; step (b) of drying theslurry yielded in step (a) to obtain a dried slurry; step (b′) ofblending the dried slurry obtained in step (b) with a solid compoundcontaining copper to obtain powders; step (c) of coating a carrier withthe powders obtained in step (b′) using a binder to obtain a coatedmolded product; and step (d) of calcining the coated molded productobtained in step (c).
 12. The method for preparing the coated catalystaccording to claim 10 or 11, wherein the compound a-4 is used as anessential component.
 13. The method for preparing the coated catalystaccording to any one of claims 10 to 12, wherein at least one speciesselected from the group consisting of water and organic compounds havinga boiling point of 150° C. or lower at one atmospheric pressure is usedas a binder.
 14. The method for preparing the coated catalyst accordingto claim 13, wherein the binder is ethanol.
 15. The method for preparingthe coated catalyst according to claim 13, wherein the binder has aweight ratio of ethanol to water being from 10:0 to 5:5.
 16. The methodfor preparing the coated catalyst according to any one of claims 10 to15, wherein the coated molded product is calcined in the presence of areducing agent in step (d).
 17. The method for preparing the coatedcatalyst according to claim 16, wherein the reducing agent is ethanol.18. A coated catalyst for producing methacrylic acid by subjectingmethacrolein, isobutylaldehyde or isobutyric acid to gas phase catalyticoxidation, obtainable from the method according to any one of claims 10to 17.